I have 10 evolution engines, including 2 100's... I like them all and they make great power. I can tune them all to be dead reliable, except 2 of the ones I have tried to mount inverted. Now, I am very familiar with inverted mounted 2 strokes and they are a fickle thing, but I still have won every battle with an inverted engine, EXCEPT THE .61NT AND THE 1.00NX! I don't know if it is the canted-back glow plug or what, but these engines are difficult to tune inverted. I have seriously tried everything I know, taking a scientific approach and seriously studying the problem, ending with nothing really conclusive to point my finger at. Glow plug type, tank height and distance, tubing diameter... nothing helped. It really had me questioning my sanity, because if all of the conditions are right, it should run fine inverted. BUT NO!!! I even used a pump to equalize the fuel draw- no effect. If I flip the plane over, they run fine. I do have an Evolution .46 that was mounted inverted in a World Models P-51 that ran like a scalded dog. The small Evo doesn't seem to care.

I ended up turning the 2 large Evo engines sideways and that fixed everything- they run great now. Let me share a few thing I have learned about these engines (many previously mentioned):

[ul][*] Make sure the carb is pushed down, making a seal with the o-ring under it... I have never had problems with this, but others have.[*] These engines must have a good bit of muffler pressure to set the carb properly. Check for leaks in the exaust, and restrict pitts mufflers as required. Important! Check it![*] The carb barrels have side-to-side play, so make sure your throttle linkage does not apply changing side loads to the barrel during movement. This will aggrevate the low speed mixture, and complicate proper adjustment. In one instance, my linkage was gently pushing in on the throttle barrel at idle, then around 50% throttle it would shift outward, causing a substantial change in the mixture. This must be why that spring is inside the carb, always pushing out on the barrel.[*] Take off all mixture stops.[*] Use a hot plug.[*] Low speed mixtures can creep. Again, never had a problem with this but others have mentioned it. They are easy to turn.[*] Make sure remtote needle valve/fuel line is not sucking air somewhere. Some people remove it altogether, but I leave them on.
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All of these symtoms kind of point to a lack-luster carburetor design, imho. They do work well though, once dialed in. My 100 that is currently installed on a plane has impeccable manners with a perfect midrange response. I can't wait to get the 1.20!